It arrived quietly nearly 200 years ago and now threatens numerous British plants, allotments, gardens, pavements, buildings, railways and water courses.

Japanese knotweed - capable of growing 3 metres in as many months - costs a fortune to control and has so far resisted attempts to stem its relentless progress.

Now researchers are sending for help to Japan, the knotweed's homeland, for a tiny bug that depends on the plant for its lifecycle. They work for Cabi, an international agricultural research body, which has been studying how Aphalara itadori, named after its host plant, might provide a solution.

Authorities in England and Wales are consulting the public on whether they should issue licences allowing the release of the bugs, alien to Britain, to see whether they can make such a meal of the dreaded knotweed that they stop its seemingly inexorable march. The bugs suck the sap during their immature, nymph stage.

Dick Shaw, one of those involved in the project, told Radio 4's Today programme that the bugs made the weed stunted and less competitive. "It is the only long-term, sustainable solution we can see. We can't continue what we are doing and doing nothing is not an option … It is not in the interests of a biocontrol agent to kill its host because then it loses its food so it tends to just suppress it."

He said the bug had "gone through very thorough pest risk analysis which is more than can be said about other invasive [species]".

Cabi says the sap-sucker emerged as the best option from more than 200 such control agents studied over six years. Tests had been made on 90 other plants, including related native species, crops and ornamental species, to check the bug did not take a liking to them too. Previous attempts at biological controls have a mixed track record. The cane toad was introduced to Australia to control pest beetles in 1935 - against scientists' recommendations - and is now a voracious threat to much else.

The harlequin ladybird was introduced in several European countries for biological control before it managed to cross the Channel and threaten British ladybirds.